Wheat Disease Update 5-29-15

Wheat Disease Update 5-29-15

Severe Levels of Stripe Rust in Wheat Fields in Southern Nebraska

Figure 3. Close-up of stripe rust-infected flag leaves showing black teleospores in a wheat field in Hitchcock County on May 28.
Figure 4. Stripe rust on a flag leaf in a wheat field in Chase County on May 28. The level of stripe rust in this field was generally low, but its development was picking up speed.
Figure 5. Barley yellow dwarf on an isolated flag leaf in a wheat field that was free of stripe rust in Chase County on May 28. Note the absence of stripe rust pustules on the leaves. This field was sprayed to control stripe rust.

May 29, 2015

A survey of wheat fields in southeast, south central, and southwest Nebraska May 27-28 showed severe levels of stripe rust. Many fields with stripe rust showed varying intensities of yellow when viewed from a distance (Figure 1). In some fields, 100% of all foliage was yellow and covered with stripe rust pustules, with only the stems and heads retaining green color (Figure 2). In some fields stripe rust had advanced to the stage where teleospores (black spores that form in later stages of rust development) were forming on the leaves (Figure 3).

Many of the fields with severe stripe rust were not sprayed with fungicide to prevent or control the disease or in isolated cases they were sprayed too late. Further west and north, stripe rust was not as severe as in the southeast or south central, but its development was picking up speed (Figure 4). Fields that were sprayed had little or no rust (Figure 5).

Estimated Yield Loss

The overall estimated yield loss due to stripe rust will not be known until later in the growing season. However, in the severely affected fields surveyed on May 27-May 28, 40% to 50% yield loss is expected. In some fields where the flag leaves were severely diseased before the beginning of grain fill, higher losses are expected.

Management

Weather conditions continue to favor stripe rust development and spread. It is too late to treat stripe rust in fields that are severely affected and especially if flag leaves have more than 50% disease severity. In wheat-growing areas further north where stripe rust is not as severe as in the southern part of the state, a fungicide spray is recommended to protect the flag leaf.

If wheat is at the full heading to the flowering growth stage, it is recommended to spray Prosaro or Caramba to both control stripe rust and suppress Fusarium head blight. A list of fungicides and their efficacies on wheat diseases is provided in a table developed by the North Central Regional Committee on Management of Small Grain Diseases (NCERA-184).

Figure 1. A wheat field with a yellow cast due to stripe rust in Nuckolls County on May 27. Many fields had varying intensities of yellow depending on the level of stripe rust severity.
Figure 2. Severe stripe rust on flag leaves in a wheat field in Hitchcock County on May 28. (Photos by Stephen Wegulo)